The present invention relates to a drafting mechanism for spinning machines for drafting a staple fiber web, a staple fiber sliver or a staple fiber slubbing. More particularly, it relates to a drafting mechanism which has at least one input roller pair, one intermediate roller pair and one output roller pair each comprising a lower roller an a pressure roller received in support elements.
Drafting mechanisms of the above-mentioned general type are known in the art. In known drafting mechanisms, staple fiber web, staple sliver and staple fiber slubbing are drafted in drafting zones each defined by two roller pairs. Each such roller pair includes a lower roller and a pressure roller which can be pressed against the lower roller. As a rule, drafting mechanisms comprise two or more drafting zones, so that at least three roller pairs are arranged one after the other with distances corresponding to the length of the drafting zones. The pressure rollers are arranged in a frame of the drafting mechanism pivotably away from the lower roller. Pressing of the pressure rollers against the lower rollers is performed by force producing means which act on the shaft bearings provided at both sides of the pressure rollers.
In order to enable adjustment of the length of the drafting zones to the requirements, the bearings which receive the lower rollers are arranged movably and fixably on rails. The same applies to the bearings which receive the pressure rollers, in that these bearings are also movable and arrestable on the frame of the drafting mechanism.
The last roller pair, as considered in transporting direction of the body of fibers, is however preferably fixedly arranged in order to avoid changes of position of these rollers relative to the subsequent elements which take up the fiber sliver or the fiber web.
If now the last drafting zone identified as the main drafting zone is to be shortened or lengthened, then the preceding roller pairs which form the break draft zones must be moved correspondingly to the same extent. When, for example two break drafting zones and one main drafting zone are provided, then during adjustment of the main drafting zone altogether three roller pairs must be displaced. This is very time-consuming.
In an arrangement in which the above-mentioned last roller pair is also arranged movably and arrestably, only the last roller pair can be displaced.
In order to perform this work more quickly, but nevertheless accurately, it is proposed in the German Published Patent Specification No. 2,852,692, that the extent of movement of the lower rollers can be read on a scale. In order to simultaneously displace the bearings of the pressure rollers associated therewith, the pressure roller is removed and a rail which, on the one hand, is adapted to the pressure roller bearings, and on the other hand, receives the lower roller, is inserted in the bearings of the pressure roller. In this manner, the lower rollers and the pressure rollers can be displaced simultaneously and to the same extent. This operation is performed for each roller pair.
A disadvantage of this method and this device, respectively, lies on the one hand, in the substitution of the pressure roller by the above-mentioned rail and remounting of the pressure roller after the displacement, and on the other hand in that in spite of this all of the roller pairs which define the break drafting zones must be adjusted one after the other.